Cold event still likely; precip threat greatly reduced

Model solutions today don’t look anywhere near as impressive as they did 48 hours ago regarding what was expected to be a very dramatic cold and wet pattern. A change to very cold weather will still occur, but not to the incredible magnitude that was forseen a few days ago. The reasons: the blocking rifge is expected to be more easterly than previously progged, and it will also be weaker, resulting in a less amplified downstream trough. This cold Arctic trough will still have a lot of very cold air with it, but the back edge will be too close to the coast to pick up much moisture. Models bring in less cold air to CA/OR/WA because northerly flow is now expected to be limited and the contribution of cold easterly flow from western Canada will be minimal. Also, the trough is not forecast to retrograde off the coast and pinch off into a very cold cut off low near CA as it was several days ago. The overall duration of the event looks to be shorter, too: Wednesday of next week to Tuesday of the following week. The most recent (00z) GFS is a little further to the west with the track of the trough, and the most recent NAM has an even more westerly track and also a stronger northerly jet. This could allow the trough to be slighly moister and colder than the 00,12, and 18z runs indicated. We’ll see if this is a trend back towards a wetter solution, but the event will likely pan out something like this:

OR/WA: Scattered to numerous convective showers and isolated thunderstorms. Snow levels 500-1000 feet Wed. dropping to sea level to 500 feet by Thurs. and Fri. Only isolated snow showers remaining for the latter part of the weekend into early next week, but lowland highs in WA and OR (Seattle + Portland inc.) could struggle to reach 35, even in direct sunshine. 

NorCal: Isolated to scattered convective showers Thurs. through Fri., esp. along coast and coastal mountains. An isolated instance of thundersnow not impossible. Snow levels dropping below 1000 feet and locally to sea level. Highs near Eureka on the coast may struggle to reach 40 in direct sunshine, and places away from the water will likely be in the 30s for much of the daytime hours. Even colder air poss. over the weekend, though flurries would probably be the extent of any precip (snow levels below 500 feet).

SoCal: Sorry, folks! Looks like mainly a cold and wind event down south, possibly mixed with some isolated to scattered showers near the coast and in the mountains if the trough takes the 00z GFS track. Snow levels dropping as low as 1000-1500 feet (2000-3000 feet in the south).

MJO is still quite active–and am not quite sure what will happen beyond days 7-10. Let’s just see what pans out in the next week, first…

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